Spontaneous emission enhanced heat transport method and structures for cooling, sensing, and power generation

ABSTRACT

A method and structure for heat transport, cooling, sensing and power generation is described. A photonic bandgap structure ( 3 ) is employed to enhance emissive heat transport from heat sources such as integrated circuits ( 2 ) to heat spreaders ( 4 ). The photonic bandgap structure ( 3 ) is also employed to convert heat to electric power by enhanced emission absorption and to cool and sense radiation, such as infra-red radiation. These concepts may be applied to both heat loss and heat absorption, and may be applied to heat transport and absorption enhancement in a single device.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method and a structure for heattransport, and more particulary to a method and a structure forspontaneous emission enhanced heat transport for cooling, sensing andpower generation. The present invention also relates to methods andstructures for cooling, sensing and power generation.

2. Discussion of the Background

For a long time the spontaneous emission of light was considered anatural and immutable property of radiating atoms. However, Purcellshowed that an atom in cavity would radiate faster than an atom in freespace (E. M. Purcell, Physical Review, 69, 681 (1946)). Purcellindicated that the spontaneous emission at wavelength λ will beincreased by a factor f given by, f˜(λ³/a³), where a is the dimension ofthe cavity. For example, Purcell suggested that incorporating metalparticles of 10⁻³ cm diameter in a matrix can cause the spontaneousemission rate at radio frequencies, 10⁷ Hz (λ˜3×10³ cm), to increase bya whopping f˜λ³/a³=(3×10³)³/(10⁻³)³˜2.7×10¹⁹ times. Thus the thermalequilibration time constant at radio frequencies will come down from5×10²¹ sec to only 3 minutes.

From Planck's radiation law, the spontaneous emission at frequency ν isderived from a probability A_(ν), given byA _(ν)˜[8πhν ³ /c ³]  (1)The above coefficient A_(ν) gets modified by the Purcell factor, f,indicated above,

Now, consider spontaneous emission at or near room temperature. Wein'sLaw gives the peak emission wavelength (λ_(T)) at a temperature T:

$\frac{\lambda_{T} - {2.89 \times 10^{- 3}\mspace{11mu}{Km}}}{T\mspace{11mu}\left( {{in}\mspace{14mu}{K.}} \right)}$

For the purpose of this discussion, consider the radiative emission atthis peak wavelength. The following equation is obtained:λ_(300k)˜9.67 μm or ν_(300k)˜3.1×10¹³ Hz.Compared to spontaneous emission at radio frequencies (ν˜10⁷ Hzdiscussed above), the probability of the spontaneous emission (at 300K)at far-infrared wavelengths (ν˜3.1×10¹³ Hz) is already high from eqn.(1). It is for this reason, all bodies are observed to radiatesignificant amount of radiation at 300K. This is the basis for imagingusing IR wavelengths.

Even though the above spontaneous emission at IR wavelengths issignificantly useful for IR imaging purposes, the energy loss(dissipative transfer) from spontaneous emission of a body even at aslightly higher temperature than 300K is rather small. The energy flux(Φ) radiating from a blackbody at temperature (T) including allfrequencies is given by the Stefan Boltzmann Law:

$\begin{matrix}{{{{where}\mspace{14mu} ɛ} = {emissivity}},{and}} & \; \\{\sigma = {{Stefan}\mspace{14mu}{Boltzmann}\mspace{14mu}{constant}}} & {= {5.672 \times 10^{- 5}\mspace{14mu}{erg}\text{/}\sec\mspace{14mu} 1\text{/}{cm}^{2}\deg^{4}}} \\\; & {= {5.672 \times 10^{- 12}\mspace{14mu} W\text{/}{cm}^{2}\mspace{14mu} 1\text{/}\deg^{4}}}\end{matrix}$For a blackbody with ε=1 at T=300K, the following is obtained:Φ≅4.39×10⁻² W/cm ²  (2)

From a heat-spreader point of view, as used in many electronics andother sensitive cooling applications around 300K, this Φ is small. Hencemost of the heat that is removed from the electronics (like a modern day1.2 GHz Pentium® processor) is achieved through a convective process(blowing air across fins) or through other conductive/heat-transferprocess (flowing liquid) as in many top-of-the-line servers andmain-frame computer electronics. These heat transfer processes are atbest modest just enough that the Pentium® chip does not overheat or thatthe reliability of the servers are not in doubt. However such solutionsare insufficient for many future cooling applications in computerelectronics operating in the 2 GHz range and above. This will beespecially true if high-performance thin-film thermoelectrics are usedto actively pump the heat from the chip, when the power density levelsthat need to be dissipated (taking into account some heat-spreadingeffects from the source to the spreader-sink side) can easily be in therange of several to tens of watts/cm². See L. H. Dubois, Proc. of18^(th) International Conference on Thermoelectrics, 1, (1999), IEEEPress. Catalog No. 99 TH8407 and references cited in this article.

For spot-cooling of high-power electronics and high-power VCSELS, simpleconvective cooling processes are insufficient. Also, the above methodsof cooling with blowing air or flowing liquid are cumbersome andintroduce unwanted complexities to systems.

SUMMARY OF THE INVENTION

It is an object of the invention to provide a method for and a structurehaving enhanced heat transfer.

It is also an object of the invention to provide a method for and astructure having enhanced heat transfer through spontaneous emission.

It is a further object of the invention to provide a method for and astructure having the ability to absorb the IR radiation efficiently thusleading to a better sensing device.

Still another object of the invention is to provide a method for and astructure having the ability to absorb the IR radiation efficiently thusleading to a better thermal-to-electrical power conversion device.

Yet another object of the invention is to provide hand-heldcomputational and communication devices with power using athermal-to-electrical power conversion device according to theinvention.

These and other objects may be obtained using a heat transfer structurehaving a heat spreader, a photonic bandgap structure connected to theheat spreader, and a defect cavity formed in the photonic bandgapstructure. A region in the heat spreader may be arranged to receive heatfrom a heat source, and the defect cavity may be positioned adjacent tothe region. A thermoelectric device may also be connected to the heatspreader.

The photonic bandgap structure may comprise an array of columnarstructures formed around the cavity. The columnar structures may have adiameter and a spacing based upon a wavelength of emitted radiation.

The photonic bandgap structure may also comprise a high thermalconductivity material with one of metal, semi-metal and semiconductorparticles disposed in the material. The particles may have an infraredtransmission property different from infrared transmission properties ofthe material. The particles may be separated in the material by one halfto three times a wavelength of an infrared emission peak correspondingto the respective temperature of the structure.

The photonic bandgap structure may also comprise microfins enhancingboth radiative and emissive heat transport.

The objects of the invention may also be obtained by a method of heattransport comprising removing heat from a heat source and using aphotonic bandgap structure to allow radiative heat transport andenhancing emissive heat transport. The method may also include steps ofdisposing a defect cavity in the photonic bandgap structure, positioningthe cavity to be aligned with heat transport from the heat source,disposing a plurality of defect cavities in the photonic bandgapstructure, and positioning a plurality of cavities to be respectivelyaligned with heat transport from plurality of heat sources.

The device according to the invention can have the photonic bandgapstructure connected to the heat spreader. The photonic bandgap structuremay also be formed as part of a heat spreader. In the case of the heatsource being an electronic integrated circuit, the photonic bandgapstructure may also be formed as a part of the substrate of theintegrated circuit or device.

The device according to the invention may also be a sensing devicehaving an infrared sensor with a sensing surface and a photonic bandgapstructure disposed to enhance coupling of infrared radiation to thesensing surface.

The device according to the invention may also be a thermal-electricconversion device comprising a heat absorption element, aheat-to-electric conversion device coupled to the element and a photonicbandgap structure disposed to enhance coupling of heat to said heatabsorption device. In a further embodiment, the device according to theinvention may comprise a sensing device having an infrared sensor and afirst photonic bandgap structure, and an infrared enhancing emissionstructure disposed to enhance emission of infrared radiation to thesensor and comprising a second photonic bandgap structure.

In yet another embodiment, a device may comprise a thermal-electricconversion device having a heat absorption element, a heat-to-electricconversion device and a first photonic bandgap structure, and a heatabsorption device and a heat enhancing emission structure disposed toenhance emission of heat to the element and comprising a second photonicbandgap structure.

The devices according to the invention may be sized to be hand-held, andthe devices according to the invention may be adapted to supplyconverted power to a hand-held electronic device. The devices accordingmay also be adapted to absorb beat from a waste heat source, such as thehand of a person.

Since good emitters are good absorbers, the concepts presented forincreased spontaneous emission are equally applicable to structuresdesigned increased absorption. Thus, these concepts are applicable tosensing of infrared radiation useful in infrared sensors as well asgeneration of electrical power based on absorbing heat radiation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1A is a diagram of a first embodiment of the device according tothe invention;

FIG. 1B is a diagram of a modification of the first embodiment of thedevice according to the invention;

FIG. 1C is a diagram of another modification of the first embodiment ofthe device according to the invention;

FIG. 1D is a diagram of another modification of the first embodiment ofthe device according to the invention;

FIG. 1E is a diagram of the device of FIG. 1A illustrating regular heatdissipation and radiative heat emission;

FIG. 1F is a diagram of the device of FIG. 1D illustrating regular heatdissipation and radiative heat emission;

FIG. 2A is a diagram of a photonic bandgap structure having a squarecavity;

FIG. 2B is a diagram of a photonic bandgap structure having a hexagonalcavity;

FIG. 2C is a diagram of a photonic bandgap structure having a circularcavity;

FIG. 2D is a perspective view of the diagram of a photonic bandgapstructure having a cavity;

FIG. 3 is a diagram illustrating the size and spacing of the arrayedstructures in a photonic bandgap structure;

FIG. 4 is a diagram of a second embodiment of the device according tothe invention;

FIGS. 5A and 5B are side and bottom diagrams, respectively, of astructure according to the invention;

FIG. 6 is a diagram of a multi-chip module according to the invention;

FIG. 7 is a diagram of a three-dimensional multi-chip module accordingto the invention; and

FIG. 8 is a diagram of a hand-held device using a heat transport deviceaccording to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

According to the invention, enhanced radiative heat transfer of heatfrom a semiconductor chip, or other device or structure requiringcooling, is obtained. This may be accomplished by integrating a photonicbandgap structure with a heat spreader or on the device or structurerequiring cooling. Spontaneous emission (at far-infrared wavelengths) isenhanced for increased radiative heat loss.

A schematic diagram of a photonic bandgap structure according to a firstembodiment integrated onto a heat spreader is shown in FIG. 1A. Here, anactive thermoelectric (TE) device 3 pumps heat from the desired region,such as active region 1, of a semiconductor device 2. Device 3 may be athin-film TE device that can pump heat at >100 W/cm² at point A. Theheat that is pumped by the TE device 3 is dumped at heat spreader 4 atpoint B. Heat spreader 4 can be made of a number of materials havinghigh thermal conductivity, such as diamond or SiC.

Heat spreader 4 is shown to have about the same dimensions of the device2, and TE device 4 is shown to have similar dimensions to active region1. This is merely for illustrative purposes and the invention is not solimited. For example, the active region may cover most of the surface ofdevice 2, and the spreader may be of smaller or larger dimensionscompared to device 2, depending upon the application, desired results orother factors.

The heat spreads from B to C, the location of the ultimate heat-sink.Going from points B to C, depending on the thermal conductivity andthickness of the spreader, the power density at C can be in the range of5 to 10W/cm² for a thin-film TE device pumping at 100 W/cm². For a bulkTE device, with a cooling power density of only 5 to 10 W/cm², the powerdensity at C would be in the 0.5 to 1 W/cm². Note that from eqn. (2)Φ≅4.39×10⁻² W/cm ²<<5 to 10 W/cm ²obtained with the conventional heat spreaders, i.e., without thephotonic bandgap/defect structure combination according to theinvention.

Attached to or incorporated into spreader 4 is a photonic bandgapstructure (PBS) 5. PBS 5 is preferably made of the same material as theheat spreader 4, but it not necessary. A PBS made of a differentmaterial could also be attached to the heat spreader in intimate thermalcontact. A defect cavity 6 may be formed at the center of PBS 5. If sucha PBS material is integrated with a defect cavity 6, as shown in FIGS.2A and 2B, then cavity 6 will show enhanced radiative heat loss at λ≅10μm. There will also be improvement at other wavelengths, for exampleλ≦10 μm. Note that the enhanced radiative property comes from theinteraction between the PBS and the adjoining cavity, where the heat isto be dissipated. Thus defect cavity 6 of PBS 5 preferably coincideswith the heat-spreading area directly below the active-heat generatingarea A as shown in FIG. 1. Such a structure is termed a SpontaneousEmission Enhanced Heat Transport (SEEHT), achieved here using photonicbandgap structures.

FIG. 1B illustrates a modification of the embodiment of FIG. 1A wherethe TE device 3 is omitted and the heat spreader 4 with PBS 5 isattached directly to the device 2, at the backside. A furthermodification is shown in FIG. 1C where the separate heat spreader isomitted and the PBS 5 is attached directly to the device 2, at thebackside. PBS 5 can be located at a position other than the backside.For example, PBS 5 and the associated defect cavity can be located abovethe active region. Lastly, FIG. 1D shows a modification where the PBS 5is formed as part of the device 2.

More detailed views are shown in FIGS. 1E and 1F. In FIG. 1E, shown withthe device of FIG. 1A is the enhanced heat dissipation 8, i.e.convective heat loss, and enhanced radiative heat emission 9. Thedissipation 8 may also contain a component from the structures in PBS 5acting as microfins (not shown). In FIG. 1E, the heat transferefficiency by the radiative process is enhanced also due to the leakageof modes from the cavity area (where heat arrives from the chip byspreading) to the PBS area similar to enhanced photoluminescenceefficiency in light emitting diodes. FIG. 1F shows the heat dissipation8 and heat emission 9 in the structure of FIG. 1D.

An example of PBS 5 according to the invention is shown in FIGS. 2A-2C.PBS 5 contains cavity 6 and photonic bandgap structures 7 consisting ofcolumnar structures spaced in an array. Cavity 6 is square in FIG. 2A,hexagonal in FIG. 2B, and circular in FIG. 2C, but it is noted thatother shapes are possible. The cavity interrupts the periodicity of thephotonic bandgap structures 7. This dramatically increases thespontaneous emission and thus dramatically increases the heatdissipation.

Also, the size of cavity 6 may be varied, depending upon theapplication. The cavity usually should be larger than the individual PBScolumnar structures to create interruption in the photonic bandgapstructure. Close packing is a consideration. Also, the size can beoptimized based upon the peak-producing area and the enhancement factorfrom the Purcell effect. The size may also be chosen in relation to thesize of source of heat or the size of the heat transfer path.

The defect cavity 6 surrounded by the photonic bandgap structure shownin FIGS. 2A and 2B can provide at least a ten-fold enhancement inspontaneous emission intensity (i.e., radiative heat loss capability)where it is needed. Higher enhancement factors can be obtained withsmaller cavity sizes, i.e., small areas where heat is generated. Inother words, the cavities can be strategically placed to remove heatfrom one or many specific areas.

FIG. 2D is a perspective cross-sectional view of PBS 5 of FIG. 2A.Structures 6 and 7 may be formed by etching the material of PBS 5 usingknown etching techniques, such as those employed in semiconductorprocessing. For example, dry or wet etching using a masking material maybe used to define structures 7. Structures 7 may be separately formedand integrated with a heat spreader.

In a more specific example illustrated in FIG. 3, for λ≅10 μm,corresponding to the peak wavelength at 300K, a, the lattice spacing forthe photonic bandgap isa/λ=0.5 or a≅5μm

-   -   and the radius r for a circular structure is        r/a≅0.45 or r≅2.25μm        Thus in FIG. 3, with a=5 μm and r≅2.25 μm, a photonic bandgap        structure with a pitch around 10 μm results. Note that although        this design is for 10 μm and the radiative emission occurs over        a broad range of wavelength around 10 μm, proportional        improvement may be expected at other wavelengths as well.

Note that this design is for λ≅10 μm, corresponding to the peakwavelength at 300K. If heat sink or device operates at highertemperatures, such as 400K, then the expected peak λ˜7.3 μm. For aboveexample, a, the lattice spacing becomes ˜3.7 μm, and r, the diameter ofthe structure would be ˜1.7 μm. Such operating temperatures are likelyto useful for high-temperature Si power electronics heat spreadingapplications and high-temperature/high-power SiC and GaN deviceapplications.

If the PBS is to be designed for lower heat sink temperatures such as77K, then the expected peak λ˜38 μm. In the above example, a would be˜19 μm, and r would be ˜8.6 μm. Obviously, such larger “a” and “r”should be easier and cheaper to achieve in practice. Such heat spreadersare likely to be useful for low-temperature applications as inlow-temperature electronics, superconducting motors and generators.

Heat spreader 4 has dimensions h₁ and h₂ shown in FIGS. 1A and 1E.Typically, in a heat spreader, it is preferable to minimize h₁ toeffectively dissipate the arriving heat at B. However, the physicalhandling of the heat spreader poses certain limitations on minimalthickness. In the heat spreader shown in FIGS. 1A and 1E, h₁ ispreferably in the range of 25 μm to 300 μm. The dimension h₂ is likelyto dominated by the consideration of the thickness of the desiredstructures that can be produced reliably. The ratio of thickness of h₂relative to h₁ can be maximized, if necessary. The dimension h₂ could bein the range of about 1-10 μm for application at 300K.

In FIG. 1D, a further modification of the FIG. 1A structure is shown,where the bottom-side of the substrate (which contains the electronics)itself is patterned to achieve similar spontaneous-emission enhancedheat removal. Of course, this avoids the use of the heat spreader aswell as the thermoelectric device. Such an arrangement is conceivable inSi-based electronics as Si, with its high thermal conductivity, canserve as the heat spreader as well as the spontaneous-emission enhancedemitter. Also, note the distinction between the heat waves and the lightwaves. Note again the distinction between the regular heat dissipationand the additional spontaneous emission enhanced light waves isindicated in FIG. 1D.

It is also conceivable that the spontaneous emission light waves couldbe absorbed by a black body absorber (not shown) that is maintained at alower temperature by a mechanism such as thermoelectric cooling orliquid cooling.

A second embodiment of an enhanced spontaneous emission device accordingto the invention is shown in FIG. 4. Conductive particles 11 areincorporated into the heat spreader to produce an enhanced radiativeheat emitter 10. As an example, approximately 2 μm particles (metal) areincorporated in a heat spreader like SiC, AlN or Si. The Purcellenhancement factor f, at ≅300K, for spontaneous radiative emission wouldbe, for λ≅10 μm and a≅2 μm:f≅λ ³ /a ³≅125Thus from eqn. (2) and the f of 125, we obtain for the structure of FIG.4:Φ≅125×4.39×10⁻² W/cm ²≅5.5W/cm ²If 1.0 micron size particles are incorporated, then the radiativeemission enhancement can be as much as a factor of 1000, over aconventional heat spreader, leading to a Φ of 44W/cm². If such micronsize particles can be incorporated by impregnation orself-assembly-followed by overgrowth, then the scope for radiative heatloss mechanisms would be considerably enhanced.

The particles 11 can be made of metal, semiconductor, semimetal in amatrix of a high-thermal conductivity heat spreader such as SiC, AIN,Si, diamond, etc. The particles 11 are preferably chosen so that theirinfrared emission characteristics are different from that of the heatspreader so that the substrate matrix and the particle do not form acontinuum from an electromagnetic emission standpoint. These emissioncharacteristics in turn can be traced to their complex refractiveindices at the wavelength of interest. It is expected that even a fewpercent difference in the refractive index between the particle and thesubstrate matrix may produce sufficient enhancement in spontaneousemission rates. A larger difference in the refractive index will alsobenefit the enhancement.

It is also preferable that the particles are separated from each other(in linear distance) by about one half to three times the wavelength ofthe IR emission peak corresponding to the respective temperature. Forexample at a temperature of 300K, with the emission peak at 10 microns,the spatial separation between adjacent 1 micron particle could beanywhere between 5 microns to 30 microns. The efficiency of theradiative emission process could depend on this spatial separation dueto the coupling between the these particles forming a continuum. Regularheat dissipation 8 and the additional spontaneous emission enhancedlight waves 9 are also indicated in FIG. 4. Note that such an orderedassemblage of micron size particles with several micron size separationmay be fabricated with epitaxial or chemical vapor deposition or simplechemical processes (like colloidal chemistry) self-assembly methods. Inaddition, in FIG. 4, thin-film thermoelectric cooling devices 3 may beincorporated (similar to FIG. 1) to combine high-cooling power densityactive-cooling with high-flux density radiative heat dissipativeprocesses.

Such spontaneous high radiative heat fluxes near 300K would make theheat-removal problem much more manageable in future electronics cooling.This could obviate the need for liquid heat transfer processes. Thus itshould be possible to make an all solid-state,spontaneous-emission-enhanced-refrigeration (SEER) systems with orwithout thermoelectric cooling devices. The thermoelectric devices wouldbe used where active cooling is needed. Certainly, these SEEHT devicesmay be necessary for thin-film devices. However, even bulkthermoelectric devices with a heat flux of about 0.5 W/cm² at theheat-sink stge could benefit from these concepts.

Another possible modification to the structure of FIG. 1A forenhancement of spontaneous emission as applied to enhanced heat removalcould be to pattern micron-sized (1 to 20 μm) structures 12 on the heatspreader 4, as shown in FIGS. 5A and 5B. No defect cavity is included.The structures double for micro-fins and thus also enhance spontaneousconvective heat loss. For example, an approximately 2 μm structure couldbe patterned on the heat spreader 4 using standard photolithographictechniques. These 2 μm geometries should be easily achievable withtoday's lithography in large-area geometries for a cost-effectiveimplementation. Note again the distinction between the regular heatdissipation and the additional spontaneous emission enhanced light wavesis indicated in FIG. 5A. Size and pattern differneces for thesestructures are anticipated based on an f≅λ³/a³—like enhancement factor.

As noted earlier, with the use of spontaneous emission enhanced heattransport structures (SEEHT) it is possible to implement effectivecooling strategies (with or without thermoelectrics) in an allsolid-state system. Such an advantage is illustrated for a multi-chipmodule in FIG. 6. Note that this schematic (showing integration in avertical direction) can be scaled in the lateral dimension as well toproduce a 3-dimensional multi-chip module (MCM). Such a 3-D MCM couldhave thermoelectric devices for cooling at various chip levels and theheat could be radiated from the periphery (both outer-ring, andinner-ring) using SEEHT structures.

Module power lines 20 and module signal line 21 are shown on spreader22. Formed on both sides of spreader 22 are PBS structures 23. In thisexample the structures are the conductive material impregnated-type PBSstructure, but it is understood that the other PBS described above mayalso be used. Thermoelectric cooling devices 24 remove heat 27 fromelectronics chip or device 25. Power is supplied to the TE devices 24 at26. Inter-level signal paths 28 and inter-level power paths 29 are alsoshown, as well as inter-level TE power connection 30 and uni-level orintra-level connection 31. Any number of arrangements are possible.

A schematic diagram of such a 3-dimensional spontaneous emissionenhanced heat transport multi-chip modules (3-D SEEHT-MCM) is shown inFIG. 7. Liquid-cooled heat-absorbing blackbody cores 40 and 41 can beincorporated inside the ring and outside the ring for absorbing theradiant heat emanating from the SEEHT structures 43 in the periphery.SEEHT structures 43 have heat spreaders with thermoelectric devices 44.Shown at 45 are SEEHT structures with conductive-particle impregnatedPBS structures. Although the SEEHT devices are shown alternating as 44and 45, other arrangements are possible. The cores are kept cooled toincrease the temperature differential between them and the SEEHTstructures, thereby enhancing radiative heat absorption. The cores couldbe appropriately coated with high-emissivity (therefore absorptivity)materials to facilitate this process. Note that the “liquid” cooling isconfined to areas where active electronics is absent. Thus, the systemcomplexity in these situations ran be considerably reduced.

The present invention offers a new approach to efficient heat spreaderstermed SEEHT using enhancement of spontaneous radiant emission of heatat long IR-wavelengths. Under certain situations these SEEHT structurescould also benefit from periodic PBS, invoking Bragg scattering therebypreventing emission trapping, specifically tailored for the longIR-wavelengths. The periodic structures around the defect cavity inFIGS. 1A-1D and 2A-2C serve this purpose and could be implementedsuitably in the SEEHT exiting surfaces of FIG. 1. Note that thedimensions of such PBS for the long-wavelengths are in the range of 2μm, considerably larger (and so easily implementable with low-costlithography) than the sub-micron features needed for the application ofPBS to LED's at the visible and near-IR wavelengths.

Two other modifications are also possible in light of the aboveteachings. One involves the use of similar concepts to obtain what canbe described as spontaneous-absorption enhanced sensors (SAES). Thisstems from the general idea that good absorbers are good dissipaters.The above described concepts to enhance energy flux radiating from ablackbody at temperature (T) are also applicable to energy flux that canbe radiatively absorbed by a blackbody at a temperature (T). This canhelp in designing improved infra-red sensors to detect temperatures ofobjects. In this case the PBS structures described above are applied tothe surface of the blackbody or sensor to enhance the absorbedradiation. Defect cavities may be used, but are not necessary ifstructures like FIG. 4 are used for enhanced absorption.

Another involves the use of similar concepts to obtain what can bedescribed as spontaneous-absoption enhanced thermal-to-electricalconverters (SAETEC). The above described concepts to enhance energy fluxradiating from a blackbody at temperature (T) are also applicable toenergy flux that can be radiatively absorbed by a blackbody at atemperature (T). This can help in designing improvedthermal-to-electrical power sources. For example, in hand-held devicesas shown in the FIG. 8, a SAETEC device can better absorb the heatradiated by the hand which in turn can be converted into electricity bydevices such as thermoelectric power converters. The heat from a hand isin the range of 10-15 W. Also, a spontaneous emission enhanced heattransport (SEEHT) device can be worn on the hand thus efficientlyradiating the heat from the palm of the hand. Thus a combination of theSEEHT device and SETEC device can be used to maximize the power fed tothe hand-held device, augmenting its battery back-up or replacing itsbattery or reducing the need for its recharging of its batteries moreoften.

The SETEC can also double as a detector, or incorporate a detector, sothat when a user picks up the hand-held device, the heat from the handis detected and actives the hand-held device.

Numerous other modifications and variations of the present invention arepossible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the presentinvention may be practiced otherwise than as specifically describedherein. For example, the PBS and SEEHT structures may be attached to orformed in devices or structures other than the semiconductor-typedevices described above. The principles of the invention are applicableto a wide range of cooling applications, devices needing cooling such asbiological devices, mechanical devices (producing heat withinthemselves), power generation devices (producing heat in various parts),piezoelectric devices, magnetic devices, optical devices, ceramicdevices and plastic devices.

1. A structure, comprising: a substrate including a heat source; a heattransfer device disposed on the substrate having a region arranged toreceive heat from the heat source; a photonic bandgap device joined tosaid heat transfer device and comprising a bandgap device materialdifferent than a susbtrate material of the substrate; and the region,the heat transfer device, and the photonic band gap device disposed inan arrangement that directs heat from the heat source through the heattransfer device to the photonic band gap device by which infraredwavelength radiation from the heat transfer device is enhanced overinfrared wavelength radiation from the heat transfer device in absenceof the photonic bandgap device.
 2. The structure as recited in claim 1,wherein the photonic bandgap device comprises a plurality of radiativeelements having respective upper surfaces opposite the heat transferdevice and side surfaces extending from a surface of the heat transferdevice, the upper and side surfaces configured to radiate infraredwavelength radiation from the photonic bandgap device.
 3. The structureas recited in claim 1, further comprising: a thermoelectric devicebetween the heat source and the region of said heat transfer device. 4.The structure as recited in claim 1, wherein said photonic bandgapdevice comprises: an array of columnar structures, said columnarstructures enhancing the infrared wavelength radiation and convectiveheat transfer from the photonic bandgap device.
 5. The structure asrecited in claim 4, comprising: said columnar structures having adiameter in the range of about 1.7-8.6 microns.
 6. The structure asrecited in claim 5, comprising: said columnar structures having adiameter of about 2.25 microns and spacing of about 5 microns.
 7. Thestructure as recited in claim 1, wherein said photonic bandgap devicecomprises: a plurality of conductive particles disposed in the bandgapdevice material.
 8. The structure as recited in claim 7, wherein: saidbandgap device material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 9. The structure as recited inclaim 7, comprising: said particles having infrared transmissionproperties different than infrared transmission properties of saidmaterial.
 10. The structure as recited in claim 7, comprising: saidparticles being separated from each other by about one half to threetimes a wavelength of an infrared emission peak corresponding to therespective temperature of said structure.
 11. The structure as recitedin claim 7, comprising: said particles having a size of about 1 micronand separated from each other by a distance between about 5 and 30microns.
 12. The structure as recited in claim 1, wherein said photonicbandgap device comprises: microfins enhancing both radiative andemissive heat transport.
 13. The structure as recited in claim 1,further comprising an active area disposed in said substrate andcomprising the heat source.
 14. The structure as recited in claim 13,comprising: a thermoelectric device disposed between said substrate andsaid heat transfer device.
 15. The structure as recited in claim 13,comprising: a plurality of active areas disposed in said substrate. 16.The structure as recited in claim 13, wherein: said heat transfer devicecomprises a first portion of said substrate; said photonic bandgapdevice comprises a second portion of said substrate; and said firstportion is disposed between said active area and said second portion.17. The structure as recited in claim 13, wherein said photonic bandgapdevice comprises: an array of columnar structures, said columnarstructures enhancing the infrared wavelength radiation and convectiveheat transfer from the photonic bandgap device.
 18. The structure asrecited in claim 17, comprising: said columnar structures having adiameter in the range of about 1.7-8.6 microns.
 19. The structure asrecited in claim 18, comprising: said columnar structures having adiameter of about 2.25 microns and spacing of about 5 microns.
 20. Thestructure as recited in claim 17, wherein said photonic bandgap devicecomprises: a plurality of conductive particles disposed in the bandgapdevice material.
 21. The structure as recited in claim 20, wherein: saidbandgap device material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 22. The structure as recited inclaim 20, comprising: said particles having infrared transmissionproperties different than infrared transmission properties of saidmaterial.
 23. The structure as recited in claim 20, comprising: saidparticles being separated from each other by about one half to threetimes a wavelength of an infrared emission peak corresponding to therespective temperature of said structure.
 24. The structure as recitedin claim 20, comprising: said particles having a size of about 1 micronand separated from each other by a distance between about 5 and 30microns.
 25. The structure as recited in claim 13, wherein said photonicbandgap device comprises: microfins enhancing both radiative andemissive heat transport.
 26. The structure as recited in claim 1,further comprising: a heat-to-electric conversion device coupled to saidheat transfer device, wherein the photonic bandgap device is disposed toenhance coupling of heat to said heat transfer device.
 27. The structureas recited in claim 26, wherein said photonic bandgap device comprises:microfins enhancing both radiative and emissive heat transport.
 28. Thestructure as recited in claim 26, wherein said photonic bandgap devicecomprises: a plurality of conductive particles disposed in the bandgapdevice material.
 29. The structure as recited in claim 28, wherein: saidbandgap device material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 30. The structure as recited inclaim 28, comprising: said particles having infrared transmissionproperties different than infrared transmission properties of saidmaterial.
 31. The structure as recited in claim 28, comprising: saidparticles having a size of about 1 micron and separated from each otherby a distance between about 5 and 30 microns.
 32. The structure asrecited in claim 26, comprising one of a hand-held computational andcommunication devices receiving converted power from saidheat-to-electric conversion device.
 33. The structure as recited inclaim 1, wherein the photonic bandgap device comprises a first photonicbandgap structure and a second photonic bandgap structure, and furthercomprising: a thermal-electric conversion device including, aheat-to-electric conversion device coupled to said heat transfer device,and the first photonic bandgap structure disposed to enhance coupling ofheat to said heat transfer device; and a heat enhancing emissionstructure disposed to enhance emission of heat to said heat transferdevice and comprising the second photonic bandgap structure.
 34. Thestructure as recited in claim 33, wherein at least one of said first andsecond photonic bandgap structures comprises: a plurality of columnarstructures formed in an array, said columnar structures enhancing theinfrared wavelength radiation and convective heat transfer from thephotonic bandgap device.
 35. The structure as recited in claim 34,wherein said at least one of said first and second photonic bandgapstructures comprises: a defect cavity disposed in said plurality ofcolumnar structures.
 36. The structure as recited in claim 33, whereinat least one of said first and second photonic bandgap structurescomprises: a plurality of conductive particles disposed in the bandgapdevice material.
 37. The structure as recited in claim 36, wherein: saidbandgap device material comprises a high thermal conductivity material;and said particles comprise one of metal, semimetal and semiconductorparticles disposed in said material.
 38. The structure as recited inclaim 36, comprising: said particles having infrared transmissionproperties different than infrared transmission properties of saidmaterial.
 39. The structure as recited in claim 36, comprising: saidparticles having a size of about 1 micron and separated from each otherby a distance between about 5 and 30 microns.
 40. The structure asrecited in claim 33, comprising: a waste heat source; and said heattransfer device absorbing heat from said waste heat source.
 41. Thestructure as recited in claim 33, comprising: said thermal-electricconversion device supplying converted power to a hand-held electronicdevice.
 42. The structure as recited in claim 41, wherein said hand-heldelectronic device comprises one of a computational or communicationdevice.
 43. The structure of claim 1, further comprising a defect cavityformed in said photonic bandgap device.
 44. The structure of claim 43,wherein: said region in said heat transfer device is arranged to receiveheat from the heat source; and said defect cavity is positioned adjacentto said region.
 45. The structure of claim 43, further comprising: athermoelectric device connected to said heat transfer device.
 46. Thestructure as recited in claim 43, wherein said photonic bandgap devicecomprises: an array of columnar structures formed around said cavity,said columnar structures enhancing the infrared wavelength radiation andconvective heat transfer from the photonic bandgap device.
 47. Thestructure as recited in claim 46, comprising: said columnar structureshaving a diameter in the range of about 1.7-8.6 microns.
 48. Thestructure as recited in claim 47, comprising: said columnar structureshaving a diameter of about 2.25 microns and spacing of about 5 microns.49. The structure as recited in claim 43, wherein said photonic bandgapdevice comprises: a plurality of conductive particles disposed in thebandgap device material.
 50. The structure as recited in claim 49,wherein: said bandgap device material comprises a high thermalconductivity material; and said particles comprise one of metal,semimetal and semiconductor particles disposed in said material.
 51. Thestructure as recited in claim 49, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 52. The structure as recited in claim 49,comprising: said particles being separated from each other by about onehalf to three times a wavelength of an infrared emission peakcorresponding to the respective temperature of said structure.
 53. Thestructure as recited in claim 49, comprising: said particles having asize of about 1 micron and separated from each other by a distancebetween about 5 and 30 microns.
 54. The structure as recited in claim43, wherein said photonic bandgap device comprises: microfins enhancingboth radiative and emissive heat transport.
 55. The structure as recitedin claim 43, further comprising: an active area disposed in saidsubstrate and comprising the heat source.
 56. The structure as recitedin claim 55, comprising: a thermoelectric device disposed between saidsubstrate and said heat transfer device.
 57. The structure as recited inclaim 55, wherein: said heat transfer device comprises a first portionof said substrate; said photonic bandgap device comprises a secondportion of said substrate; and said first portion is disposed betweensaid active area and said second portion.
 58. The structure as recitedin claim 55, wherein said photonic bandgap device comprises: an array ofcolumnar structures formed around said defect cavity, said columnarstructures additionally enhancing convective heat transfer from thephotonic bandgap device.
 59. The structure as recited in claim 58,comprising: said columnar structures having a diameter in the range ofabout 1.7-8.6 microns.
 60. The structure as recited in claim 59,comprising: said columnar structures having a diameter of about 2.25microns and spacing of about 5 microns.
 61. The structure as recited inclaim 58, wherein said photonic bandgap device comprises: a plurality ofconductive particles disposed in the bandgap device material.
 62. Thestructure as recited in claim 61, wherein: said bandgap device materialcomprises a high thermal conductivity material; and said particlescomprise one of metal, semimetal and semiconductor particles disposed insaid material.
 63. The structure as recited in claim 61, comprising:said particles having infrared transmission properties different thaninfrared transmission properties of said material.
 64. The structure asrecited in claim 61, comprising: said particles being separated fromeach other by about one half to three times a wavelength of an infraredemission peak corresponding to the respective temperature of saidstructure.
 65. The structure as recited in claim 61, comprising: saidparticles having a size of about 1 micron and separated from each otherby a distance between about 5 and 30 microns.
 66. The structure asrecited in claim 55, wherein said photonic bandgap device comprises:microfins enhancing both radiative and emissive heat transport.
 67. Thestructure as recited in claim 43, further comprising: a heat-to-electricconversion device coupled to said heat transfer device, wherein thephotonic bandgap device is disposed to enhance coupling of heat to saidheat transfer device.
 68. The structure as recited in claim 67, whereinsaid photonic bandgap device comprises: a plurality of columnarstructures formed in an array, said columnar structures enhancing theinfrared wavelength radiation and convective heat transfer from thephotonic bandgap device.
 69. The structure as recited in claim 68,wherein said defect cavity is disposed in said plurality of columnarstructures.
 70. The structure as recited in claim 67, wherein saidphotonic bandgap device comprises: a plurality of conductive particlesdisposed in the bandgap material.
 71. The structure as recited in claim70, wherein: said bandgap device material comprises a high thermalconductivity material; and said particles comprise one of metal,semimetal and semiconductor particles disposed in said material.
 72. Thestructure as recited in claim 70, comprising: said particles havinginfrared transmission properties different than infrared transmissionproperties of said material.
 73. The structure as recited in claim 70,comprising: said particles having a size of about 1 micron and separatedfrom each other by a distance between about 5 and 30 microns.
 74. Thestructure as recited in claim 67, comprising one of a hand-heldcomputational and communication devices receiving converted power fromsaid heat-to-electric conversion device.
 75. The structure as recited inclaim 43, wherein the photonic bandgap device comprises a first photonicbandgap structure and a second photonic bandgap structure, and furthercomprising: a thermal-electric conversion device including, aheat-to-electric conversion device coupled to said heat transfer device,and the first photonic bandgap structure disposed to enhance coupling ofheat to said heat transfer device; and a heat enhancing emissionstructure disposed to enhance emission of heat to said heat transferdevice and comprising the second photonic bandgap structure.
 76. Thestructure as recited in claim 75, wherein at least one of said first andsecond photonic bandgap structures comprises: a plurality of columnarstructures formed in an array, said columnar structures enhancing theinfrared wavelength radiation and convective heat transfer from thephotonic bandgap device.
 77. The structure as recited in claim 76,wherein the defect cavity is disposed in said plurality of columnarstructures.
 78. The structure as recited in claim 75, wherein at leastone of said first and second photonic bandgap structures comprises: aplurality of conductive particles disposed in the bandgap material. 79.The structure as recited in claim 78, wherein: said bandgap devicematerial comprises a high thermal conductivity material; and saidparticles comprise one of metal, semimetal and semiconductor particlesdisposed in said material.
 80. The structure as recited in claim 78,comprising: said particles having infrared transmission propertiesdifferent than infrared transmission properties of said material. 81.The structure as recited in claim 78, comprising: said particles havinga size of about 1 micron and separated from each other by a distancebetween about 5 and 30 microns.
 82. The structure as recited in claim74, comprising: a waste heat source; and said heat transfer deviceabsorbing heat from said waste heat source.
 83. The structure as recitedin claim 74, comprising: said thermal-electric conversion devicesupplying converted power to a hand-held electronic device.
 84. Thestructure as recited in claim 83, wherein said hand-held electronicdevice comprises one of a computational or communication device.
 85. Astructure, comprising: a solid state electronic device; a substratesupporting the solid state electronic device and providing a heattransfer mechanism to conduct heat from the solid state device; aphotonic bandgap device joined to said substrate and including astructured-material having a plurality of radiative elements spacedapart by which infrared wavelength radiation from the substrate isenhanced over infrared wavelength radiation from the substrate inabsence of the photonic bandgap device; and said solid state electronicdevice, substrate, and photonic bandgap device disposed in anarrangement that directs heat from the solid state device through thesubstrate to the photonic bandgap device, wherein the structuredmaterial comprises a material different than a material of thesubstrate.
 86. The structure as recited in claim 85, further comprising:a multichip module including the solid state device, the substrate, andother circuitry; and said photonic bandgap device is configured toenhance radiation of heat from the multichip module.
 87. The structureas recited in claim 85, further comprising: a heat-to-electricconversion device coupled to said substrate.
 88. The structure asrecited in claim 87, wherein the heat-to-electric conversion devicecomprises a thermoelectric element.
 89. A structure, comprising: a heattransfer device having a region arranged to receive heat from a heatsource; a photonic bandgap device joined to said heat transfer device; athermoelectric device between the heat source and the region of saidheat transfer device; and the region, the heat transfer device, thethermoelectric device, and the photonic band gap device disposed in anarrangement that directs heat from the heat source through the heattransfer device through the thermoelectric device to the photonic bandgap device by which infrared wavelength radiation from the heat transferdevice is enhanced over infrared wavelength radiation from the heattransfer device in absence of the photonic bandgap device.
 90. Astructure, comprising: a heat transfer device having a region arrangedto receive heat from a heat source; a photonic bandgap device joined tosaid heat transfer device; a heat-to-electric conversion device coupledto said photonic bandgap device; and the region, the heat transferdevice, the photonic band gap device, and the heat-to-electricconversion device disposed in an arrangement that directs heat from theheat source through the heat transfer device through the photonic bandgap device to the heat-to-electric conversion device by which infraredwavelength radiation from the heat transfer device is enhanced overinfrared wavelength radiation from the heat transfer device in absenceof the photonic bandgap device.